1. Field of Invention
This invention relates generally to computing systems. Specifically, a method and apparatus for managing power delivered by way of a FireWire cable to a battery operated peripheral device.
2. Description of Related Art
FireWire is an IEEE1394 compliant High Performance Serial Bus that provides two types of data transfer: asynchronous and isochronous. Asynchronous is for traditional load-and-store applications where data transfer can be initiated and an application interrupted as a given length of data arrives in a buffer. Isochronous data transfer ensures that data flows at a pre-set rate so that an application can handle it in a timed way while providing the bandwidth needed for audio, imaging, video, and other streaming data. Isochronous service means it guarantees latency or the length of time between a requested action and when the resulting action occurs which is a critical feature in supporting real time video, for example. FireWire provides a high-speed serial bus with data transfer rates of 100, 200, or 400 Mbps as well as a single plug-and-socket connection on which up to 63 devices can be attached with data transfer speeds up to 400 Mbps (megabits per second). In this way, FireWire offers a standard, simple connection to all types of consumer electronics, including digital audio devices, digital VCRs and digital video cameras; as well as to traditional computer peripherals such as optical drives and hard disk drives.
The standard FireWire cable consists of six wires in which data is sent via two separately-shielded twisted pair transmission lines that are crossed in each cable assembly to create a transmit-receive connection. Two more wires carry power (8 to 28 v, 1.5 A max.) to remote devices. In some cases, such as with DV camcorders manufactured by the Sony Corporation of Japan, a 4 conductor FireWire cable is used (configured as the 6 wire cable but without the power wires) that terminate in smaller, 4 prong connectors. To connect a four prong device, such as the Sony DV camcorder with a standard IEE1394 FireWire device or interface card, an adapter cable is required having 4 prongs on one side and 6 on the other. In this way, the data lines are connected while omitting the power connection.
In those situations, however, when a battery operated six prong peripheral device is coupled to a FireWire cable, it is important for the power delivered to the device (typically 1.8 v, 3.3, or 5.0 v) to be both stable and reliable especially when the FireWire cable is either connected or disconnected.
Therefore, what is required is a method and apparatus for managing power delivered by way of a FireWire cable to a battery operated peripheral device.